This invention relates to a carburetor which comprises, in addition to an ordinary carburetor arrangement, a fully automatic starter suction system adapted to operate at the start and during the warming-up of the engine.
Automatic starting devices for carburetors known in the art are roughly classified into two groups; those in one group depend on a choke valve, bimetallic thermostat or the like for the control as described in U.S. Pat. No. 2,124,778, and those in the other group are of the starter valve type which have an auxiliary fuel system independent of the main so that auxiliary fuel can be automatically fed through a mixed charge passage communicated with a carburetor space downstream from the throttle valve. When a device of the former group is employed, human assistance is still necessary. Since the opening of the throttle valve for fast idling is determined by a cam mechanism operable in accordance with choke opening, the operator, when starting the engine, must depress the accelerator pedal to open the throttle valve to a predetermined extent so as to set the fast idle opening. Also, during the warming-up period, the operator has to shift the fast idle cam position and control the throttle opening toward a closing position in order to control the maximum engine speed. When the engine is allowed to warm up with an existing carburetor starting device of the character, the unchanged throttle opening presents a noise problem because it increases the engine speed with the progress of warming-up. To avoid this, the accelerator pedal must be depressed to shift the fast idle cam position once the warming-up has proceeded to a certain point. The devices of the first group are thus not fully automatic in controlling the operation from the start to the conclusion of warming-up of the engine.
Also, because the choke valve located on the upstream side of the nozzle is used to increase the vacuum in the vicinity of the main nozzle for more fuel feed, the rate of suction air flow in front of the main nozzle is not high enough to ensure full atomization of the fuel. This calls for a large supply of fuel for the starting purpose with no small sacrifices of fuel economy and cleanness of the exhaust.
The latter group of the starter valve type feeds fuel by dint of intake vacuum or negative pressure, and therefore has common problems of imperfect gastightness of the starter valve and inadequate controllability of the air-fuel ratio at the cold start and during warming-up. In addition, the starter valves are in many cases disk valves and involve such great frictional forces that, in the case of automatic starting devices using bimetallic thermostats or the like, it has been difficult to ensure the uniformity of quality.